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III. — On the History , Histological Structure , and Affinities of 
Nematophycus Logani, Carr. ( Prototaxites Logani, Dawson), 
an Alga of Devonian Age. By Wm. Carruthers, F.R.S., &c. 
Plates XXXI. and XXXII. 
Sir "Wm. Logan, in his ‘ Report on the Progress of the Canadian 
Geological Survey for 1844,’ published an account of his discovery 
of fossil plants in beds of Devonian age at Gaspe, in Lower Canada. 
In 1856 Dr. Dawson described, in the ‘ Proceedings of the American 
Association’ (p. 174), one of the most interesting of these fossils — 
a stem which he considered exhibited a very remarkable and pre- 
viously undescribed coniferous structure. With the view of more 
thoroughly investigating Logan’s discovery he visited Gaspe in 
1859, and published in the ‘ Quarterly Journal of the Geological 
Society ’ * a lengthened description of the plants. Among them was 
the stem already referred to, for which he established the genus 
Prototaxites. The description of the fossil then given is as follows : 
— “Woody trunks with concentric rings of growth, and medullary 
rays. Cells of pleurenchyma scarcely in regular series, thick-walled 
and cylindrical, with a double series of spiral fibres. Disk-structure 
indistinct in the specimen observed.” The name was given to the 
stem because of the “ spirally-marked cells characteristic of the 
genera Taxites and Spiropitys of Goppert, but differing from any 
conifer known to me in the cylindrical form and loose aggregation 
of the wood cells, as seen in the cross-section.” In the lengthened 
description Dr. Dawson says that in longitudinal section “ the wood 
cells are seen to be much elongated, and to terminate in conical 
points, and their sides are covered with the remains of a double 
series of spiral fibres, among which are a few scattered roundish 
spots, which perhaps indicate a single row of disks.” No pith is 
perceptible, and the medullary rays are marked hy clear, structure- 
less spaces, the cells having been entirely disorganized; but the 
EXPLANATION OF PLATES XXX. AND XXXI. 
Plate XXXI. — Containing transverse sections of Nematophycus Logani , Carr. 
Fig. a, showing across the centre of the specimen the tract of smaller cells, which 
gives the exogenous aspect to the stem ; and an open space with a few scattered 
tubes, — a medullary ray of Dr. Dawson. Fig. b, a part of the open space in a. 
The artist has produced the effect shown hy using the binocular microscope with 
a deep objective. Fig. c, a part of a, showing tho spaces between the tubes and 
the mouths of the smaller tubes. 
Plate XXXII. — Containing longitudinal sections of Nematophycus Logani , 
Carr. Fig. a, showing the irregular direction of the tubes, and a few tubes in the 
clear space, or “medullary ray.” Fig. b, a small fragment, showing a series of 
sub-circular markings on the inner surface of a cell — the “ bordered pores ” of 
Dr. Dawson. Fig. c, a part of a, showing the large longitudinal tubes, and the 
multitude of smaller tubes matting them together. 
Vol. xv . p. 477. 
